Until the present, an aircraft pilot was dependent upon visual contact with an approaching aircraft and upon voice advisories from ground based traffic controllers to avoid mid-air collision with another aircraft There is currently being implemented a Traffic Alert and Collision Avoidance System (TCAS) which will enable a lone aircraft to develop a panoramic display of surrounding aircraft equipped with Air Traffic Control Radar Beacon System (ATCRBS) transponders.
Document RTCA/DO-185 "Minimum Operational Performance Standards for Traffic Alert and Collision Avoidance System", published September, 1983, by the Radio Technical Commission for Aeronautics, Washington, D.C., 20005 broadly describes TCAS in the following terms:
TCAS is most readily understood by visualizing its operation in flight. When airborne, the TCAS equipment periodically transmits interrogation signals. These interrogations are received by Air Traffic Control Radar Beacon System (ATCRBS) or Mode S altitude reporting transponders. In reply to the interrogations, the transponder transmits a signal which reports its altitude. The TCAS equipment computes the range of the intruding aircraft by using the round-trip time between the transmission of the interrogation and the receipt of the reply.
Altitude, altitude rate, range and range rate are determined by tracking the reply information. These data, together with the current TCAS sensitivity level (which specifies the protected volume around the aircraft) are used to determine whether the intruding aircraft is a threat. Each threat aircraft is processed individually to permit selection of the minimum safe resolution advisory based on track data and coordination with other TCAS-equipped aircraft
If the threat detection logic in the TCAS computer determines that a proximate aircraft represents a potential collision or near-miss encounter, the computer threat resolution logic determines the appropriate vertical maneuver that will ensure the safe separation of the TCAS aircraft. The appropriate maneuver is one that ensures adequate vertical separation while causing the least deviation of the TCAS aircraft from its current vertical rate.
The resolution advisories displayed to the pilot can be divided into two categories: Corrective advisories, which instruct the pilot to deviate from the current flight path (e.g. DON'T CLIMB when the aircraft is climbing); and preventive advisories (e.g. DON'T CLIMB when the aircraft is in level flight).
The traffic advisories displayed to the pilot describe the positions of proximate aircraft that are, or could become, collision threats. The display of traffic advisories alerts the flight crew to the presence of threat, or potential threat aircraft, and may improve the ability of the crew to respond to subsequent resolution advisories. In addition, traffic advisories may improve the ability of the flight crew to visually acquire the traffic.
The referenced DO-185 standard provides that the following information shall be displayed to the flight crew. The means for displaying such information are not specified.
a. Resolution Advisories:
CLIMB PA1 DESCEND PA1 DON'T CLIMB PA1 DON'T DESCEND PA1 DON'T CLIMB FASTER THAN 500 FPM PA1 DON'T CLIMB FASTER THAN 1000 FPM PA1 DON'T CLIMB FASTER THAN 2000 FPM PA1 DON'T DESCEND FASTER THAN 500 FPM PA1 DON'T DESCEND FASTER THAN 1000 FPM PA1 DON'T DESCEND FASTER THAN 2000 FPM
b. Failure of own TCAS equipment
c. TCAS equipment inhibited--either automatically or through crew action
d. Encounter situation worsened beyond limits of resolution by TCAS equipment.
In addition to the information specified in Paragraphs a-d above, display of traffic advisories for at least three targets including range, altitude and bearing of intruding aircraft is required.
It is vital that the information provided by TCAS be presented to the flight crew in the most effective manner to ensure prompt and correct reaction by the crew. At present, TCAS traffic advisories, together with the resolution advisories CLIMB, DESCEND, DON'T CLIMB, DON'T DESCEND are displayed on a cathode ray tube (CRT) which may be either dedicated to TCAS display or shared for the display of information from sources other than TCAS, such as weather radar.
The remaining TCAS resolution advisories DON'T CLIMB FASTER THAN 500 FPM, DON'T DESCEND FASTER THAN 500 FPM, etc. are displayed on the Instantaneous Vertical Speed Indicator (IVSI). The IVSI is a standard flight instrument which combines the output of a barometric altitude rate sensor with the integrated output of a vertical accelerometer. Data from the vertical accelerometer compensates for the time lag in the data from the barometric rate sensor.
In its most common form the rate of climb or descent of the aircraft sensed by the IVSI is indicated by the position of a pointer on a circular scale. In a less common form, the altitude rate is indicated by the position of a pointer along a linear scale.
Those TCAS resolution advisories requiring the aircraft to climb or descend at a limited rate are displayed on the IVSI by illuminating with red light the portion of the background of the IVSI indicator scale at which rates the aircraft flight path is not to be changed. For example, if the TCAS resolution advisory is DON'T CLIMB FASTER THAN 1000 FPM, the background of the IVSI indicator climb scale for rates of 1000 FPM and greater is illuminated red while the climb scale for rates from zero to 1000 FPM and the descent scale for all rates continue to be illuminated normally. Such a display of TCAS resolution advisories creates the possibility that the flight crew may not interpret the advisory as a positive command to alter flight course immediately or that the crew may misinterpret the advisory and react in an incorrect manner. Further, since the present means of displaying TCAS resolution advisories involves separate displays for certain of the advisories, the crew must first focus attention on the area of the instrument panel containing the traffic advisory display, then refocus attention on the area of the instrument panel containing the IVSI display. The necessity for thus shifting attention to obtain a complete TCAS resolution advisory creates the possibility that some event may divert the crew's attention long enough to delay reaction to the advisory beyond the time during which proper reaction would resolve the collision threat.
It is an object of the invention to provide means for displaying in a single unit all traffic advisories and resolution advisories generated for display by TCAS.
It is another object of the invention to provide a unitary display for TCAS traffic advisories and resolution advisories in which the information is presented in an unambiguous and readily comprehensible manner.
It is a further object of the invention to provide a unitary display for TCAS traffic advisories and resolution advisories in which the information is presented symbollically to the maximum extent possible.